For cold water corals, warming is beating acidification to drive a growth spurt

New research shows that the surface temperature of the ocean dictates how well …

The release of excess CO2 from the combustion of fossil fuels, deforestation, and other processes doesn’t just affect our air; it also affects our oceans. The oceans absorb as much as 30 percent of the excess carbon dioxide in the atmosphere, which lowers their pH. Thus, our emissions have two large consequences for our oceans: warmer temperatures and increased acidity.

These changes may have a profound effect on coral growth, since corals are sensitive to both temperature and pH. There is mounting evidence that coral health has been declining in recent years. But what, exactly, is affecting coral? A new study in Science shows that current changes in coral growth may have more to do with the ocean’s temperature than its pH.

Corals, which gain nutrients through a symbiotic process with algae, pull calcium from the ocean to create protective layers, a process known as “calcification.” Over time, these layers accumulate and grow into what we call coral reefs. Scientists have hypothesized that the recent declines in the coral health at many well-known reefs were caused by the decreasing pH of the oceans, which can make it harder for coral to use calcium from the surrounding water. If ocean acidification is the driving force behind these declines, corals in cold, high-latitude areas should be affected first, since lower-temperature waters are more subject to acidification.

To examine coral growth in the reefs inhabiting the waters off the western coast of Australia, a team of researchers took 27 core samples from six populations of coral. The samples spanned 11 degrees of latitude in the Indian Ocean; some of the populations lived in cold, high-latitude waters, while others lived in warmer parts of the ocean closer to the equator. From the cores, the scientists could look at various aspects of the coral’s growth over the last 110 years.

The scientists found that the calcification rate of the corals did depend on the location, but not in the direction that the ocean acidification hypothesis would predict. The two southernmost populations showed definite increases in calcification since 1900, up to a 23.7 percent increase in one location. Among the more northern populations, four showed no change in calcification over time, and two showed decreases in calcification rates. If ocean acidification were driving these trends, the southernmost waters would be more prone to lowered pH in that region, and corals there would show decreased calcification.

Instead, the calcification rates have more to do with temperature than acidification. The scientists compared changes in the sea surface temperature at each location to the changes in calcification rates. Coral populations where the sea had warmed the most (those living in the coldest water) actually had the largest increases in calcification rates, and populations with smaller increases in sea surface temperature (where the sea was warmer to begin with) either had no change in calcification or underwent declines.

The results show that temperature may have a larger impact on coral growth than acidification does, at least in this set of samples. Rather than be adversely affected by warming oceans, coral reefs in cold water take advantage of higher temperatures that bring them closer to optimal growth conditions. However, temperature increases in other locations may put the water over the ideal temperature for coral growth. This may either cause declines in calcification directly, or leave them susceptible to acidification.

Due to the diversity of coral species and the large geographic range in which they live, corals aren’t responding uniformly to climate change. Furthermore, the effects are likely to change over time; even though some populations are benefitting initially from changes in temperature, these advantages will likely disappear as the warming process continues.

Kate Shaw Yoshida
Kate is a science writer for Ars Technica. She recently earned a dual Ph.D. in Zoology and Ecology, Evolutionary Biology and Behavior from Michigan State University, studying the social behavior of wild spotted hyenas. Emailkate.shaw@arstechnica.com//Twitter@KateYoshida

I don't doubt global warming or that it is connected to human activity.

But I have no idea why all effects of climate change have to be negative and that anything that might look like it could be positive must be couched in terms that assure us that this positive impact is surely temporary and doom will resume soon.

I don't doubt global warming or that it is connected to human activity.

But I have no idea why all effects of climate change have to be negative and that anything that might look like it could be positive must be couched in terms that assure us that this positive impact is surely temporary and doom will resume soon.

Good point. I think it's a result of the defensiveness that comes from constantly being under attack by a group of people who aren't actually interested in the science.

I don't doubt global warming or that it is connected to human activity.

But I have no idea why all effects of climate change have to be negative and that anything that might look like it could be positive must be couched in terms that assure us that this positive impact is surely temporary and doom will resume soon.

Can you give an example of a positive effect of climate change? One that comes to mind is the warming of locations closer to the poles (Canada, etc.), which would allow for agriculture in areas that previously would have been too cold for crops to grow. That could be seen as a positive but the socioeconomic cost in moving the infrastructure (people, roads, etc.) needed to process these crops would be astronomical.

...even though some populations are benefitting initially from changes in temperature, these advantages will likely disappear as the warming process continues.

Nice article, but the ending stuck out as unscientific guesswork. In an article that is reporting observational evidence that directly contradicts scientific conventional wisdom, to summarize with MORE conventional wisdom without evidence is really poor form and makes one question the impartiality of the author.

...even though some populations are benefitting initially from changes in temperature, these advantages will likely disappear as the warming process continues.

Nice article, but the ending stuck out as unscientific guesswork. In an article that is reporting observational evidence that directly contradicts scientific conventional wisdom, to summarize with MORE conventional wisdom without evidence is really poor form and makes one question the impartiality of the author.

It's not guesswork. We have known for quite some time that coral bleaching events can be caused by elevated temperatures. We also have extensive experimental evidence that acidification results in a net loss of carbonate reef (people have actually pumped CO2 into areas of the seafloor that they have mechanically isolated to simulate, say, a 700ppm CO2 atmosphere). The sentence is well supported by experimental and observational evidence.

Here's a suggestion for you and others who tend to respond to something that doesn't make sense to you: ask questions before you go making accusations of "poor form" and question the impartiality of the author, ask a question. We're usually happy to engage with honest questions, and we'll fix things we have wrong. Accusations like the ones you're making really don't serve any purpose that i can see, other than possibly making you happy for some reason.

I don't doubt global warming or that it is connected to human activity.

But I have no idea why all effects of climate change have to be negative and that anything that might look like it could be positive must be couched in terms that assure us that this positive impact is surely temporary and doom will resume soon.

Can you give an example of a positive effect of climate change? One that comes to mind is the warming of locations closer to the poles (Canada, etc.), which would allow for agriculture in areas that previously would have been too cold for crops to grow. That could be seen as a positive but the socioeconomic cost in moving the infrastructure (people, roads, etc.) needed to process these crops would be astronomical.

As is the cost of reducing the effects of climate change. In the end, we will likely need to do a bit of both.

...even though some populations are benefitting initially from changes in temperature, these advantages will likely disappear as the warming process continues.

Nice article, but the ending stuck out as unscientific guesswork. In an article that is reporting observational evidence that directly contradicts scientific conventional wisdom, to summarize with MORE conventional wisdom without evidence is really poor form and makes one question the impartiality of the author.

It's not guesswork. We have known for quite some time that coral bleaching events can be caused by elevated temperatures. We also have extensive experimental evidence that acidification results in a net loss of carbonate reef (people have actually pumped CO2 into areas of the seafloor that they have mechanically isolated to simulate, say, a 700ppm CO2 atmosphere). The sentence is well supported by experimental and observational evidence.

Here's a suggestion for you and others who tend to respond to something that doesn't make sense to you: ask questions before you go making accusations of "poor form" and question the impartiality of the author, ask a question. We're usually happy to engage with honest questions, and we'll fix things we have wrong. Accusations like the ones you're making really don't serve any purpose that i can see, other than possibly making you happy for some reason.

I would also point out that the statement is a very sound interpretation of the results of the experiment in the article. As colder waters warmed, the coral got closer to ideal growth temperature, and grew faster. As warmer waters warmed, the coral was still in, or got farther from ideal growth temperature, which further made it more susceptible to acidification, resulting in slower growth and some degradation. The logical conclusion is that if the trend continues, the cold waters, that are now warm, will eventually reach peak growth temperature, and then start going past it resulting in a decline, as seen in the waters that started warmer.

I honestly don't see any guesswork here, so much as a sound, testable hypothesis, logically reached based on the evidence and the assumption that a trend will continue (and assuming a trend will continue is kind of one of the first things you do when evaluating potential impact of a trend...).

...even though some populations are benefitting initially from changes in temperature, these advantages will likely disappear as the warming process continues.

Nice article, but the ending stuck out as unscientific guesswork. In an article that is reporting observational evidence that directly contradicts scientific conventional wisdom, to summarize with MORE conventional wisdom without evidence is really poor form and makes one question the impartiality of the author.

It's not guesswork. We have known for quite some time that coral bleaching events can be caused by elevated temperatures. We also have extensive experimental evidence that acidification results in a net loss of carbonate reef (people have actually pumped CO2 into areas of the seafloor that they have mechanically isolated to simulate, say, a 700ppm CO2 atmosphere). The sentence is well supported by experimental and observational evidence.

Here's a suggestion for you and others who tend to respond to something that doesn't make sense to you: ask questions before you go making accusations of "poor form" and question the impartiality of the author, ask a question. We're usually happy to engage with honest questions, and we'll fix things we have wrong. Accusations like the ones you're making really don't serve any purpose that i can see, other than possibly making you happy for some reason.

You can't have your cake and eat it too. This study seems to directly contradict the expectations created by the earlier studies, and is based more on actual "in situ" observational data rather than mechanical/experimental simulations. This goes directly to the fact that the earth is almost impossible to model- there are so many feedbacks that counter-intuitive reality is almost always going to trump predictive models.

If you want to directly contradict the most recent and apparently solid observational evidence by throwing off a sentence at the end of a story you have to do better than an appeal to authority.

Just to let you know ocean acidification is the thing that has most had me worried about CO2 emissions- its something I've accepted and been concerned about since it first came into public discussion. I still object to your 'poor form' though in this instance...

Anyone who has kept fish in an aquarium knows that changing pH is a disaster for fish and all aquatic life, corals included. I don't think the possible total collapse of marine fisheries is an acceptable trade off for any benefit, you won't be able to replace that loss by growing more wheat in Canada.

I'm not saying that all of these *will* happen, but they might. In the case of Greenland, we know that it was inhabited 1000 years ago.

You wouldn't necessarily get longer growing seasons. CO2 is only one factor related to plant growth, sunlight is another one. As the food generating areas move northward, there is less direct sunlight to spur plant growth and days become shorter pretty quickly towards the fall.

As far as Greenland goes, wtf are you talking about? It's been largely covered by ice for well over a million years, middle-age Scandinavian propaganda notwithstanding. Yeah, there were some settlements along the coast. Guess what, there still are. Also, guess what happens to sea levels if all of the ice melts off Greenland: buh bye much of Florida.

I'm not saying that all of these *will* happen, but they might. In the case of Greenland, we know that it was inhabited 1000 years ago.

Umm. Greenland is inhabited NOW....

Secondly, learn some botany. CO2 in general doesn't boost plant growth more than slightly, because the VAST majority of plants are NOT limited in their growth by available CO2. You can ENGINEER situations in which that is the case, largely by adding lots of water, specially controlled quantities of fertilizer, and specialized artificial lighting that's even more intense than sunlight at ground level.... On the plants that won't just die when you try.

But generally, just no. Plants are incredibly good at extracting CO2 from the air, and increasing CO2 concentration WILL NOT make them grow faster. EDIT: The point which is critical above is that plants are usually limited by energy availability and/or nutrients, long before the CO2 becomes an issue.

...even though some populations are benefitting initially from changes in temperature, these advantages will likely disappear as the warming process continues.

Nice article, but the ending stuck out as unscientific guesswork. In an article that is reporting observational evidence that directly contradicts scientific conventional wisdom, to summarize with MORE conventional wisdom without evidence is really poor form and makes one question the impartiality of the author.

It's not guesswork. We have known for quite some time that coral bleaching events can be caused by elevated temperatures. We also have extensive experimental evidence that acidification results in a net loss of carbonate reef (people have actually pumped CO2 into areas of the seafloor that they have mechanically isolated to simulate, say, a 700ppm CO2 atmosphere). The sentence is well supported by experimental and observational evidence.

Here's a suggestion for you and others who tend to respond to something that doesn't make sense to you: ask questions before you go making accusations of "poor form" and question the impartiality of the author, ask a question. We're usually happy to engage with honest questions, and we'll fix things we have wrong. Accusations like the ones you're making really don't serve any purpose that i can see, other than possibly making you happy for some reason.

You can't have your cake and eat it too. This study seems to directly contradict the expectations created by the earlier studies, and is based more on actual "in situ" observational data rather than mechanical/experimental simulations. This goes directly to the fact that the earth is almost impossible to model- there are so many feedbacks that counter-intuitive reality is almost always going to trump predictive models.

If you want to directly contradict the most recent and apparently solid observational evidence by throwing off a sentence at the end of a story you have to do better than an appeal to authority.

Just to let you know ocean acidification is the thing that has most had me worried about CO2 emissions- its something I've accepted and been concerned about since it first came into public discussion. I still object to your 'poor form' though in this instance...

Your reading comprehension was lacking. The assumptions mentioned in the article were based on the relationship between acidification and water temperature. The result that was different from expected was the amount that temperature played as a component of growth, compared to the effect of acidification to inhibit growth.

As to your assertion that you cannot model the earth, your logic is flawed. It's not about feedback or counter-intuitive reality (take a look at quantum mechanics, basically everything there is counter-intuitive, and we manage accurate -- or as accurate as quantum anything can be lol -- predictions there just fine). What it is about is not understanding all the variables and their impact on each other. As our understanding of these grows, we're better able to make more accurate predictions, and model the earth. Hell, even look to weather reports: they're a hell of a lot more accurate now than when I was a kid, and that has very much to do with improvements both in our understanding and in computing power to crunch the numbers. On the note of weather, I think I remember reading several years ago how we could predict the weather with nearly 100% certainty, but to reach that level of certainty took longer than from the time of the readings were taken to the time the prediction applied to, lol (but again, this was several years ago, and many generations of CPU).

And again, that sentence is a perfectly logical conclusion based on the observations of the experiment, which is what the article is about, first and foremost: THIS experiment.

I don't doubt global warming or that it is connected to human activity.

But I have no idea why all effects of climate change have to be negative and that anything that might look like it could be positive must be couched in terms that assure us that this positive impact is surely temporary and doom will resume soon.

Can you give an example of a positive effect of climate change? One that comes to mind is the warming of locations closer to the poles (Canada, etc.), which would allow for agriculture in areas that previously would have been too cold for crops to grow. That could be seen as a positive but the socioeconomic cost in moving the infrastructure (people, roads, etc.) needed to process these crops would be astronomical.

As is the cost of reducing the effects of climate change. In the end, we will likely need to do a bit of both.

Agreed. I was just trying to point out that any foreseen benefits of climate change also come with negatives, and that most (all?) of those negatives are greater than the positives.

I would also point out that the statement is a very sound interpretation of the results of the experiment in the article. As colder waters warmed, the coral got closer to ideal growth temperature, and grew faster. As warmer waters warmed, the coral was still in, or got farther from ideal growth temperature, which further made it more susceptible to acidification, resulting in slower growth and some degradation. The logical conclusion is that if the trend continues, the cold waters, that are now warm, will eventually reach peak growth temperature, and then start going past it resulting in a decline, as seen in the waters that started warmer.

I honestly don't see any guesswork here, so much as a sound, testable hypothesis, logically reached based on the evidence and the assumption that a trend will continue (and assuming a trend will continue is kind of one of the first things you do when evaluating potential impact of a trend...).

Lets parse exactly what was said in the last paragraph:

"Due to the diversity of coral species and the large geographic range in which they live, corals aren’t responding uniformly to climate change."

Agreed.

"Furthermore, the effects are likely to change over time;"

True, but ambiguous and unknowable.

"even though some populations are benefitting initially from changes in temperature"

Point he is about to discount.

"these advantages will likely disappear as the warming process continues."

Why? This is a large claim without any supporting evidence, other than the writers opinion, hence an unscientific appeal to authority. He isn't quoting the authors of the study but inserting his opinion. Previous to this study he would of had the weight of evidence behind him and it would have been an /uncontroversial/ opinion, now it is just an opinion. The study only showed minor negatives for increased temperature and apparently major benefits for coral populations in colder climes.

When the scientific consensus that acidification was going to be a major driver in halting coral growth is now disproven and a NEW hypothesis that temperature is the major driver barely on the table (and the evidence so far that it is a net contributor to coral growth), the author of the article is INSTANTLY ready to declare this a BAD THING. I just don't get how this follows.

"these advantages will likely disappear as the warming process continues."

Why? This is a large claim without any supporting evidence, other than the writers opinion, hence an unscientific appeal to authority. He isn't quoting the authors of the study but inserting his opinion. Previous to this study he would of had the weight of evidence behind him and it would have been an /uncontroversial/ opinion, now it is just an opinion. The study only showed minor negatives for increased temperature and apparently major benefits for coral populations in colder climes.

Because if the trend continues, the situation observed for the first group is precisely what will happen to the second as their temperature warms further, and all other evidence indicates that the trend is continuing. No opinion needed.

I'm not saying that all of these *will* happen, but they might. In the case of Greenland, we know that it was inhabited 1000 years ago.

Besides being worng about plant growth and Greenland as others have pointed, you are forgetting that while npolar regions may become more inhabitable, other areas will become uninhabitable (tropical areas suffering from desertification, coastal areas being submersed, among others).

You can't have your cake and eat it too. This study seems to directly contradict the expectations created by the earlier studies, and is based more on actual "in situ" observational data rather than mechanical/experimental simulations.

I just told you that there are many other studies that show that elevated ocean temperatures are responsible for coral bleaching. Those are just as "in situ" as this study. Do you think that somehow they don't count now that this study has been published?

markstewart wrote:

If you want to directly contradict the most recent and apparently solid observational evidence by throwing off a sentence at the end of a story you have to do better than an appeal to authority.

Again, you're making assumptions about what we're doing that are simply not accurate. We're not trying to directly contradict anything - we're trying to place this current study within the context of the existing body of scientific research. Because, you know, that's what the actual scientists will be doing. In order to do so, we're not appealing to anyone - we're just summarizing what the best available understanding is, without going into excessive detail that would distract from the focus on the existing study.

When the scientific consensus that acidification was going to be a major driver in halting coral growth is now disproven and a NEW hypothesis that temperature is the major driver barely on the table (and the evidence so far that it is a net contributor to coral growth), the author of the article is INSTANTLY ready to declare this a BAD THING. I just don't get how this follows.

I think i see what one of the problems is here. Read my post immediately above - this new information will be integrated with all the other information we already had, and our overall perspective will be modified accordingly. Nothing's been disproven; this one finding does not somehow obviate all the previous findings that elevated temperatures and lowered pH can both harm corals. We can use this new finding to adjust our understanding without throwing everything that came before it out.

I don't know if you've been reading too much Thomas Kuhn, but most of science does not proceed through revolutions. The predominate mode of progress is to modify existing ideas as new data comes in, rather than starting from scratch with each new result.

When the scientific consensus that acidification was going to be a major driver in halting coral growth is now disproven and a NEW hypothesis that temperature is the major driver barely on the table (and the evidence so far that it is a net contributor to coral growth), the author of the article is INSTANTLY ready to declare this a BAD THING. I just don't get how this follows.

I think i see what one of the problems is here. Read my post immediately above - this new information will be integrated with all the other information we already had, and our overall perspective will be modified accordingly. Nothing's been disproven; this one finding does not somehow obviate all the previous findings that elevated temperatures and lowered pH can both harm corals. We can use this new finding to adjust our understanding without throwing everything that came before it out.

I don't know if you've been reading too much Thomas Kuhn, but most of science does not proceed through revolutions. The predominate mode of progress is to modify existing ideas as new data comes in, rather than starting from scratch with each new result.

But that isn't what the you wrote in the body of the article:

"If ocean acidification were driving these trends, the southernmost waters would be more prone to lowered pH in that region, and corals there would show decreased calcification.

Instead, the calcification rates have more to do with temperature than acidification."

In other words acidication was a MINOR variable. Temperature was the major variable. And it lead to a large increase in productivity in cold climes.

Unless and until we quantify how much new territory becomes viable and or much more productive due to temperature increase and compare and contrast that to the relatively minor effects of temperature increase in warmer areas we cannot know the end result.

TFA wrote:

The two southernmost populations showed definite increases in calcification since 1900, up to a 23.7 percent increase in one location. Among the more northern populations, four showed no change in calcification over time, and two showed decreases in calcification rates.

You didn't quantify the loss in the two decreased areas, but I assume it was proportionally less than the 23% increase. Most sites showed no change. They likely didn't test areas that are now productive for coral that weren't even candidates previously due to the obvious fact that they COULDN'T support coral previously. To me it is obvious than one cannot say that the net effect of higher temperatures is eventually negative unless one says that the temperature increase will be open-ended with no ceiling, in which case coral will be the least of our problems...

It's not guesswork. We have known for quite some time that coral bleaching events can be caused by elevated temperatures. We also have extensive experimental evidence that acidification results in a net loss of carbonate reef (people have actually pumped CO2 into areas of the seafloor that they have mechanically isolated to simulate, say, a 700ppm CO2 atmosphere). The sentence is well supported by experimental and observational evidence.

It's my understanding that the ph problem comes from the speed the the Co2 is introduced. So how is it a good test to "simulate" 700ppm in such a manner? This doesn't seem like it would be a good test as it bypasses the natural buffering that occurs.

The two southernmost populations showed definite increases in calcification since 1900, up to a 23.7 percent increase in one location. Among the more northern populations, four showed no change in calcification over time, and two showed decreases in calcification rates.

Based on this statement, could we hypothesize that the coral in colder water actually BENEFITED from more CO2 in the water? The coral in the colder southern waters (southern hemisphere, remember) actually INCREASED calcification.

It's not guesswork. We have known for quite some time that coral bleaching events can be caused by elevated temperatures. We also have extensive experimental evidence that acidification results in a net loss of carbonate reef (people have actually pumped CO2 into areas of the seafloor that they have mechanically isolated to simulate, say, a 700ppm CO2 atmosphere). The sentence is well supported by experimental and observational evidence.

It's my understanding that the ph problem comes from the speed the the Co2 is introduced. So how is it a good test to "simulate" 700ppm in such a manner? This doesn't seem like it would be a good test as it bypasses the natural buffering that occurs.

There's a couple of things going on here. The rate of change influences the supersaturation of carbonates, which in turn influences how readily they can be incorporated into skeletal/shell/etc. material. Carbonates, however, also simply dissolve under acidic conditions. So, it's a partial model - informative, but not definitive.

I don't know if you've been reading too much Thomas Kuhn, but most of science does not proceed through revolutions. The predominate mode of progress is to modify existing ideas as new data comes in, rather than starting from scratch with each new result.

But that isn't what the you wrote in the body of the article:

"If ocean acidification were driving these trends, the southernmost waters would be more prone to lowered pH in that region, and corals there would show decreased calcification.

Instead, the calcification rates have more to do with temperature than acidification."

In other words acidication was a MINOR variable. Temperature was the major variable. And it lead to a large increase in productivity in cold climes.

Unless and until we quantify how much new territory becomes viable and or much more productive due to temperature increase and compare and contrast that to the relatively minor effects of temperature increase in warmer areas we cannot know the end result.

How is what i said contradictory to what's in the article? We need to modify our global understanding to accommodate the new information we have about what goes on specifically in cold water areas. Once again, we do not throw out the big picture, which includes what we already know about warm water corals.

When the scientific consensus that acidification was going to be a major driver in halting coral growth is now disproven and a NEW hypothesis that temperature is the major driver barely on the table (and the evidence so far that it is a net contributor to coral growth), the author of the article is INSTANTLY ready to declare this a BAD THING. I just don't get how this follows.

Pardon, but how does the finding that a few high-latitude reefs in cool waters benefited more from rising temperatures than were hurt by acidification "disprove" that acidification will be a "major driver" on the global scale? Where are most of the reefs on the planet?

markstewart wrote:

Unless and until we quantify how much new territory becomes viable and or much more productive due to temperature increase and compare and contrast that to the relatively minor effects of temperature increase in warmer areas we cannot know the end result.

Assumptions:1- It will be easy for corals to find ideal and uninhabited locations at the right depth, with all the necessary conditions, as temperature zones shift.2- Reefs will be able to migrate at the same rate that temperature zones shift, keeping up with the Red Queen.3- The warming in equatorial reefs (which has caused plenty of major bleaching events that have destroyed reefs in the last 20 years) will be "minor", while the warming of cool-water reefs will apparently be "major" by comparison.

I don't doubt global warming or that it is connected to human activity.

But I have no idea why all effects of climate change have to be negative and that anything that might look like it could be positive must be couched in terms that assure us that this positive impact is surely temporary and doom will resume soon.

Can you give an example of a positive effect of climate change? One that comes to mind is the warming of locations closer to the poles (Canada, etc.), which would allow for agriculture in areas that previously would have been too cold for crops to grow. That could be seen as a positive but the socioeconomic cost in moving the infrastructure (people, roads, etc.) needed to process these crops would be astronomical.

I disagree about your assessment of the cost. As we get more areas we can use to grow crops in Canada, our farming industry grows. There's already people and roads all over this country, we exploit natural resources all the way to Resolute Bay in the arctic circle, no biggie, climate change is mostly making things easier in those areas.

Some issues crop up for areas where ice roads were commonly used, and there's the massive boom in pests like mosquitos but it's definitely not an "astronomical" cost at any rate.

Based on this statement, could we hypothesize that the coral in colder water actually BENEFITED from more CO2 in the water? The coral in the colder southern waters (southern hemisphere, remember) actually INCREASED calcification.

No, they apparently benefited from an increased temperature. Introducing more CO2 without raising the temperature likely wouldn't have have helped corals calcify their skeletons (I mean, how would that even work?).

Based on this statement, could we hypothesize that the coral in colder water actually BENEFITED from more CO2 in the water? The coral in the colder southern waters (southern hemisphere, remember) actually INCREASED calcification.

No, they apparently benefited from an increased temperature. Introducing more CO2 without raising the temperature likely wouldn't have have helped corals calcify their skeletons (I mean, how would that even work?).

The southern corals are in COOLER water. Cool water will hold more CO2.

Based on this statement, could we hypothesize that the coral in colder water actually BENEFITED from more CO2 in the water? The coral in the colder southern waters (southern hemisphere, remember) actually INCREASED calcification.

No, they apparently benefited from an increased temperature. Introducing more CO2 without raising the temperature likely wouldn't have have helped corals calcify their skeletons (I mean, how would that even work?).

The southern corals are in COOLER water. Cool water will hold more CO2.

Yes, but it's not the CO2 that helped the corals. It's the warming water.